1. Field of the invention
the present invention relates to fluid compressors. In particular, the invention relates to a fluid compressor used in a refrigerating circuit for compressing refrigerant, for example.
2. Description of the Related Art
In recent years, various fluid compressors which have an enhanced sealing ability with a relatively simple construction and thus are easily assembled have been considered. One example of such fluid compressors is shown in FIG. 1. A conventional fluid compressor 11 includes a casing 13, compressing unit 15 located in casing 13 and a driving unit 17, i.e., a motor for driving compressing unit 15. Driving unit 17 includes an annular stator 19 fixed to the inner circumferential surface of casing 13 and an annular rotor 21 arranged inside stator 19. Rotor 21 is fixed to the outer circumferential surface of a cylinder 23 of compressing unit 15 arranged in casing 13 coaxially with casing 13. The outer surface of rotor 21 faces the inner circumferential surface of stator 19 separated a distance from each other.
One of the open ends of cylinder 23 is rotataly supported and airtightly closed by a main bearing 25 fixed to the corresponding end of casing 13. The other end of cylinder 23 is also supported and airtightly closed by an auxiliary bearing 27 fixed to the corresponding end of casing 13. In this case, the other end of cylinder 23 is elastically supported by an elastic support element 29 disposed between the inner circumferential surface of cylinder 23 and the outer circumferential surface of auxiliary bearing 13. Thus, the other end of cylinder 23 can be moved within a certain extent.
A columnar rotary rod 31, the diameter of which is smaller than the inner diameter of cylinder 23, is arranged in the axial direction of cylinder 23. Rotary rod 31 is located with its central axis A eccentric by the distance e with respect to the central axis B of cylinder 23. A part of rotary rod 31 is in contact with the inner circumferential surface of cylinder 23 along the axial direction thereof. Rotary rod 31 acts as a piston in compressing unit 15. The right end portion of rotary rod 31 is rotatably inserted in bearing hole 25a formed in main bearing 25. The left end of rotary rod 31 also is rotatably inserted in bearing hole 27a of auxiliary bearing 27. These bearing holes 25a and 27a are coaxially fromed with one the other and are eccentrically located by the distance e to the axis of cylinder 23.
As shown in FIG. 1, rotational force transmitting mechanism Sa is provided at the right end portion of rotary rod 31. Rotational force transmitting mechanism Sa includes a rectangular section 33 formed to main shaft 31a of rotary rod 31, an Oldham-ring 35 and an Oldham-ring receiver 37 shown in FIG. 2. A relative rotation is carried out between cylinder 23 and rod 31 (piston) when cylinder 23 is rotationaly driven by driving unit 17. This is because the rotational force is transmitted from cylinder 23 to rotary rod 31 through rotational force transmitting mechanism Sa.
The construction of the conventional rotational force transmitting mechanism Sa will be described in more detail with reference to FIG. 2. Main shaft 31a (the right end portion), whose diameter is smaller than that of rotary rod 31, coaxially extends from rotary rod 31. As stated above, main shaft 31a is rotatably inserted in bearing hole 25a of main bearing 25. The above-described rectangular section 33 is formed at the extending base portion of main shaft 31a. The width and length (a direction perpendicular to the width direction) of rectangular section 33 in cross-section are the same, i.e., a, and are substantially equal to or slightly greater than the diameter d.phi. of main shaft 31a. Oldham-ring 35 is formed in a disc shape of a certain thickness, and the diameter thereof is substantially equal to that rotary rod 31. A rectangular-shaped hole 39 is formed at the central portion of Oldham-ring 35. The length of hole 39 is substantially equal to that of rectangular section 33, as indicated in an alphabetical symbol a, and the width thereof is greater than that of rectangular section 33, as indicated in an alphabetical symbol b in FIG. 2. First and second opposite rectangular grooves 41a and 41b are formed in one surface of Oldham-ring 35 at opposite sides of hole 39 along the length direction of hole 39.
The above-described Oldham-ring receiver 37 is formed in a disc shape whose diameter is substantially equal to the inner diameter of cylinder 23 so that the outer edge surface of receiver 37 is fixed to the inner circumferential surface of cylinder 23. A rectangular-shaped guide hole 43 is formed at the central portion of receiver 37. The width and the length of guide hole 43 are the same and are equal to the width of hole 39 of Oldham-ring 35, as indicated in an alphabetical symbol b in FIG. 2. First and second opposite rectangular projections 45a and 45b are integrally formed on the surface of Oldham-ring receiver 37 at opposite sides of guide hole 43 along the length direction of hole 43. First and second opposite rectangular projections 45a and 45b are slidably fitted into the corresponding first and second grooves 41a and 41b, respectively when Oldham-ring 35 is mounted on Oldham-ring receiver 37. Assembled Oldham-ring 35 and Oldham-ring receiver 37 are mounted on main shaft 31a through holes 39 and 43 and holes 39 and 43 are finally engaged with the outer surface of rectangular section 33. Then, rotary rod 31 on which Oldham-ring 35 and Oldham-ring receiver 37 are assembled is inserted into cylinder 23 and Oldham-ring receiver 37 is fixed to a prescribed position in cyldinder 23.
A spiral groove 47 is formed on the circumferential surface of rotary rod 31. Spiral groove 47 extends from one end to the other end of rotary rod 31. As shown in FIG. 1, the pitch of spiral groove 47 is gradually narrowed with a distance from the suction side (right end) toward the discharge side (left end) of rotary rod 31.
A spiral blade 49 is fitted in spiral groove 47. The thickness of spiral blade 49 is substantially the same as the width of groove 47 and blade 49 is movable along groove 47 in the radial direction of rotary rod 31. The outer surface of blade 49 slide s on the inner circumferential surface of cylinder 23 while it is forcibly in contact therewith.
The space between the inner circumferential surface of cylinder 23 and the outer circumferential surface of rotary rod 31 is divide into a plurality of operation chambers 51 by spiral blade 49. Each operation chamber 51 is defined by two adjacent turns of spiral blade 49. The volumes of operation chambers 51 are gradually reduced from the suction side toward the discharge side of cylinder 23.
A suction hole 53 extends through main bearing 25 in the axial direction of cylinder 23. One of the ends of suction hole opens inside cylinder 23 and the other end is connected to a suction tube 55 of a refrigerating circuit (not shown) for a fluid communication.
A discharge hole 57 is formed in a portion of cylinder 23 close to auxiliary bearing 27. One end of hole 57 opens the inside of operation chamber 51 having a smallest volume and the other end thereof opens the inside of casing 13. A discharge tube 59 is connected to casing 13 for a fluid communication.
The construction of a thrust force cancel system will be described. A first pressure pass 61 is formed in main bearing 25. One end of first pressure pass 61 opens the inside casing 13 and the other end opens bearing hole 25a of main bearing 25. A second pressure pass 63 is formed in rotary rod 31. One end of second pressure pass 63 opens bearing hole 27a of auxiliary bearing 27 and the other end opens one of the operating chambers 51a defined by the edge surface of main bearing 25 and spiral blade 49. The suction pressure in one of the operational chambers 51a is supplied to bearing hole 27a through second pressure pass 63 and thus the suction pressure (smaller than the discharge pressure) is applied to the edge surface of auxiliary shaft 31b. The discharge pressure in casing 13 also is supplied to bearing hole 25a through first pressure pass 61 and thus the discharge pressure (greater than the suction pressure) is applied to the edge surface of main shaft 31a.
In the above-describe conventional fluid compressor 11, when driving unit 17 is energized, cylinder 23 is rotated as rotor 21 rotates. The rotational force of cylinder 23 is transmitted to rotary rod 31 through rotational force transmitting mechanism Sa, and blade 49 also is rotated together with cylinder 23. While rotating, blade 49 maintains the contact between the outer surface thereof and the inner circumferential surface of cylinder 23. Therefore, each part of blade 49 is pushed successively into groove 47 as it becomes closer to each contact point between the outer circumferential surface of rod 31 and the inner circumferential surface of cylinder 23 and emerges from groove 47 as it goes away from the contact point. Meanwhile, as compressing unit 15 is operated, a gaseous refrigerant is drawn into cylinder 23 through suction tube 55 and suction hole 53. The gaseous refrigerant from suction tube 55 is first confined in one of the operating chambers 51a nearest to the suction end of cylinder 23. The gaseous refrigerant confined in operating chamber 51 is transmitted toward the discharge side and is compressed, as rotary rod 31 rotates. The compressed gaseous fluid is finally discharge into the inside of casing 13 through discharge hole 57.
In the construction of the above-described conventional fluid compressor, Oldham-ring 35 and Oldham-ring receiver 37 of rotational force transmitting mechanism Sa are inserted from the edge of main shaft 31a and are moved along main shaft 31a to engage with rectangular section 33. However, such inserting and moveing operations are troublesome.
Furthermore, in the above-described compressing operation, since a gaseous refrigerant is compressed along the axial direction of cylinder 31, a thrust force acts on rotary rod 31 from the discharge side toward the suction side (from the left hand side toward the right-hand side in FIG. 1). Rotary rod 31 is pushed toward main bearing 25 by the thrust force and is in contact with main bearing 25. A frictional losses occur by the sliding rotation between rotary rod 31 and main bearing 25.
However, since the conventional fluid compressure 13 employs the thrust force cancel system, the discharge pressure is applied to the edge surface of main shaft 31a through first pressure pass 61 and the suction pressure is applied to the edge surface of auxiliary shaft 31b through second pressure pass 63. A force occurs in the direction reverse to that of the thrust force, and thus the force is balanced with thrust force.
It is required to increase the area of the edge surface of main shaft 31a to increase the pressure acting on the edge surface of main shaft 31a. However, since Oldham-ring 35 and Oldham-ring receiver 37 are assembled through main shaft 31a, the width and length of rectangular section 33 should be increased if the diameter d.phi. of main shaft 31a is increased. On the other hand, if the inner diameter of cylinder 23 is increased, the external shape of fluid compressor 11 is also increased. Thus, it is undesirable to increase the inner diameter of cylinder 23. This means that it is difficult to increase the diameter of Oldham-ring 35 and Oldham-ring receiver 37. However, if the diameter of main shaft 31a is increased, it is necessary to increase the diameter of Oldham-ring 35 and Oldham-ring receiver 37 to form hole 39 and guide hole 43.
When the above-described circumstances are taken into consideration, it is difficult to increase the diameter of main shaft 31a in the conventional fluid compressor.